Various bonuses
Enter 735S653J or 585A926D as a code. This will unlock extra money for equipment in Single Player mode, extra money for character unlocking in Multi-player mode, silver weapons in Multi-player mode, and the Superb Ranger weapon that can be used during the first two chapters.

Very Hard difficulty
Successfully complete Single Player mode.

Avoid losing momentum
Jumping and switching weapons while in mid-air is a good way to help keep your current speed and momentum. This helps a lot if you find yourself being chased by someone in a multi-player game and are low or out of ammunition for your current weapon.

Trophies
Complete the following tasks to unlock PlayStation3 trophy rewards.
Act I (Bronze): Complete Act I.
Act II (Bronze): Complete Act II.
Act III (Bronze): Complete Act III.
Act IV (Bronze): Complete Act IV.
Crowbait (Bronze): Finish the game on at least easy difficulty.
Between Hay and Grass (Bronze): Finish the game on at least medium difficulty.
D-Day (Bronze): On chapter I, destroy all rafts before they land.
Catcher in the Rye (Bronze): On chapter II, in the field, kill enemy soldiers using knives without being detected.
Yankee Cow (Bronze): On chapter II, don't kill the cow.
Mayhem (Bronze): On chapter III, kill 20 armed enemies while riding the stagecoach.
Sharpshooter Distraction (Bronze): On chapter IV, playing as Ray, kill sharpshooters without Thomas' help.
Sharpshooter Destruction (Bronze): On chapter IV, playing as Thomas, kill sharpshooters in 10 seconds.
Quite a Ride (Bronze): On chapter IX, on the lift, destroy everything that is thrown at you.
Rowing-Race Cheater (Bronze): On chapter XI, kill all the Indians during canoe chase.
Man of the Hood (Bronze): On chapter XII, playing as Thomas, use only bow throughout the whole level.
Boy Scout (Bronze): Finish one side quest.
Shield of Hope (Bronze): Finish all side quests.
Quick Hands (Bronze): Kill 7 people during one concentration mode.
Frag Steal (Bronze): Kill all enemies in a single Cooperative Concentration Mode.
Arkansas Fried Rooster (Bronze): Blow up 10 chickens with dynamite.
Fireworks (Bronze): Shoot 2 enemy dynamite sticks in mid air.
None Shall Hide (Bronze): Shoot an enemy through a wall.
Mad Carpenter (Bronze): Kill 5 enemies with a chair.
Vindicator (Bronze): Kill a total of 30 enemies with movable gatling.
99 Scalps (Bronze): Deliver 99 headshots (ranked play counts).
Pistol Expert (Bronze): Kill 250 People using pistols (ranked play counts).
Rifle Expert (Bronze): Kill 250 People using rifles (ranked play counts).
Shotgun Expert (Bronze): Kill 250 People using shotguns (ranked play counts).
High Noon (Bronze): Kill 4 enemies between 12:00 p.m. and 12:15 p.m. (local time, ranked play counts).
Drive-By (Bronze): Kill a total of 5 enemies while horseback (ranked play counts).
Welcome to the Frontier (Bronze): Finish a full Wild West Legends game (ranked only).
Crime Does Pay (Bronze): Win 5 rounds as an Outlaw (ranked only).
Tin Star (Bronze): Win 5 rounds as a Lawman (ranked only).
Jack of All Trades (Bronze): Play a full game with each class (ranked only).
Well Invested (Bronze): Buy 20 second level and 10 third level upgrades (ranked only).
Unforgiven (Bronze): Kill 10 enemies as an invincible wanted (ranked only).
Curly Wolf (Silver): Finish the game on hard difficulty.
Ray's Story (Silver): Finish every chapter playing as Ray.
Thomas' Story (Silver): Finish every chapter playing as Thomas.
Gotta Catch'em All (Silver): Collect all secrets.
Untouchable (Silver): Finish any chapter, except for VI and VIII, without getting severely wounded.
On the Right Track (Silver): Collect a total of $200 000 (ranked play counts) to unlock silver weapons in multiplayer.
Been There, Done That (Silver): Play a full Wild West Legends game on every level (both match and revenge match count; ranked only).
Magnificent Thirteen (Silver): Unlock all classes (ranked only).
Old West Legend (Gold): Finish the game on very hard difficulty.
Goldrush! (Gold): Collect a total of $1 000 000 (ranked play counts) to unlock golden weapons in multiplayer.
Forgiveth Me, Lord (Gold): Kill 2000 enemies (ranked play counts).
Ace of Spades (Platinum): Collect all other trophies.